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Old 2005-08-11, 12:11   #1
Kosmaj
 
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Nov 2003

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Default A minor bug in PRP-24.14

I'm testing the latest PRP-24.14 and I found a minor bug.
On start-up when the output file is created (to write PRPs) the sieve limit is truncated to lower 32 bits. For example, the first line of my input file is:
837001000000:M:0:2:258

but the output file reads
3777344576:M:1:2:258

and Mod(837001000000, 2^32)=3777344576.

This is not important but I wonder how reliable is the PRP testing part. Last year there was a bug there so serious testing is required. OTOH, that's not so easy when new PRP versions are being released almost every month. So far I only tested 17 known k*2^n-1 primes and all were successfully detected.
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Old 2005-08-29, 14:46   #2
Cruelty
 
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Have you tested 24.14 some more? I wonder if there is a possibility for PRP to "miss" a prime and what would be the probability of such event...
I am right now at ~110k with 736320585 and I am looking for a way (other than newpgen) to speed it up - PRP is faster than LLR - the question is: how reliable it is?
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Old 2005-08-29, 15:14   #3
Kosmaj
 
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I did more tests on 24.14 but nothing substantial, just about 20 primes k*2^n-1, one half k<300 and the other "15k" like k's (10^8-10^9), n in the 200-300k range, and all were correctly found to be PRPs. I stopped tests because I found that on my Pentium-M laptop PRP-24.14 performs almost the same like the latest LLR. Maybe it's faster on P-4. To answer your question, with a high probability the PRP test part is bug-free because no bugs were reported since last year. But it's impossible to be certain until we have a stable version and more people interested in testing it.

BTW, you can go straight to n=200k, the small guys cannot be reported to Top-5000 and the probability to find a Sophie-Germain by chance at n=100k is miniscule. If you are interested in SG you have to sieve specifically for SG (or "lucky minus"), such options are available in NewPGen.
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Old 2005-08-29, 20:28   #4
Cruelty
 
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I'm planning to make it a comprehensive search from 0 to 1M
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